1. Field of the Invention
This invention relates generally to phased array antennas generating one or more beams simultaneously and, more particularly, to a phased array antenna for simultaneously generating multiple beams having a common phase center using phase-only control.
2. Description of Related Art
RF transmit systems having the capability of covering two or more areas of operation simultaneously with the same information are generally well known. Examples of such systems include: navigational systems, such as the emerging GPS-III global positioning system, where improved accuracy is achieved by illuminating two different areas of operation with a tight beam at enhanced RF power levels; communications systems that are required to concurrently relay the same information to two or more locations; and, electronic warfare (EW) systems having capability of simultaneously jamming multiple hostile sites.
Navigational systems, such as the GPS-III system, require that the phase center be maintained whether a single or multiple beam mode of operation is in place.
Where such systems include an electronically scanned array (ESA), the antenna is typically divided into two or more sub-arrays that implement separate apertures, each covering a given area of operation. For a two beam system, a xe2x88x923 dB aperture penalty is paid as well as a 3 dB radiated power penalty that totals 6 dB in degradation. Moreover, a coincident phase center for the mobile beams is lost by the separation of the antenna into separate sub-arrays due to the fact that the beam generated by each sub-array has its own phase center. This separation of phase centers limits the accuracy obtainable, particularly when used in a global positioning system.
Accordingly, it is an object of the present invention to provide an improvement in electronically scanned arrays, such as phased array antennas.
It is another object of the present invention to provide an improvement in phased array antennas generating and radiating two or more RF signals.
It is a further object of the present invention to optimize the effective radiated power of a phased array antenna system.
It is another object of the invention to provide a phased array antenna which improves accuracy in a navigational or global positioning system.
These and other objects are achieved by an electronically scanned phased array antenna system which utilizes phase-only control in the generation of multiple beams simultaneously having a coincident or common phase center so that the entire aperture is used to radiate available RF energy, thus using all of the RF power that the aperture can radiate.
In one aspect of the invention, it is directed to a method of simultaneously generating two or more beams of RF energy for transmission by an array of radiator elements of a phased array including respective RF signal phase shifters coupling RF energy to each element of the array, comprising the steps of: generating respective phase control signals for each phase shifter associated with each radiator element of the array in response to a direction command for generating a separate phase front for each beam of said two or more beams; combining the respective phase control signals for each said radiator element for each beam of said two or more beams so that the phase fronts have a common phase center; coupling only the phase information resulting from combining the respective phase controlled signals for each said radiator element for each beam of said two or more beams so that the phase fronts have a common phase center to respective phase shifters associated with each of the radiators of the array for steering the phase fronts of the beams in respective predetermined directions.
In another aspect of the invention, it is directed to a phased array antenna system for simultaneously generating at least two beams of RF energy having a common phase center by phase-only control, comprising: an RF signal source; a plurality of radiator elements arranged in an array; a beamformer network coupling the RF signal source to the plurality of radiator elements; respective RF phase shifters coupled between the beamformer network and each radiator of said plurality of radiator elements for varying the respective phase of an RF signal radiated from the radiator elements; a source of direction command signals; and beam steering circuitry including, means for generating phase control signals for each of the respective phase shifters in response to a direction command signal generated by said source of direction command signals for generating a separate phase front for each of said beams and wherein the phase fronts have a common phase center, means for combining the respective phase control signals for each of the phase shifters for each of said beams so as to form composite phase control signals for each of said radiator elements, and means for setting the amplitudes of the composite phase control signals so as to be substantially equal, said composite phase control signals of substantially equal amplitude being coupled to said phase shifters so as to provide phase-only steering of said beams simultaneously in respective predetermined directions from the same radiator elements.
Further scope of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood, however, that the detailed description and specific example, while disclosing the preferred embodiment of the invention, is provided by way of illustration only, since various changes and modifications coming within the spirit and scope of the invention will become apparent to those skilled in the art.